In a wireless communication system (e.g., an Orthogonal Frequency Division Multiple Access (OFDMA) system or a Single Carrier-Frequency Division Multiple Access (SC-FDMA) system), radio resources are considered to be the set of consecutive sub-carriers, and are defined by a two-dimensional (2D) time-frequency region (also called a 2D time-frequency domain).
A single time-frequency region is denoted by a rectangle decided by time coordinates and sub-carrier coordinates. In other words, a single time-frequency region can be denoted by a rectangle defined by both a symbol of at least one time axis and a sub-carrier of several frequency axes. The time-frequency region may be allocated to an uplink of a specific user equipment (UE). In a downlink, a base station (BS) (also called a Node-B) may transmit the time-frequency region to a specific UE.
In order to define the above-mentioned time-frequency domain in a two-dimensional (2D) space, a predetermined number of OFDM symbols must be provided to the time domain, and a predetermined number of consecutive sub-carriers must be provided to the frequency domain such that the consecutive sub-carriers will begin at a predetermined position which is spaced apart from a reference point of the frequency domain by a predetermined offset.
In an Evolved Universal Mobile Telecommunications System (E-UMTS) system, radio frames of 10 ms have been used, and a single radio frame includes 20 sub-frames. In other words, the single radio frame corresponds to 0.5 ms. A single resource block includes a single sub-frame and 12 sub-carriers. Each of the 12 sub-carriers includes a band of 15 kHz. A single sub-frame includes several OFDM symbols. Some parts (e.g., a first symbol) of the several OFDM symbols may be used to transmit L1/L2 control information.
FIG. 1 is a conceptual diagram illustrating a physical channel structure for use in the E-UMTS system. A single sub-frame includes a hatched part serving as an L1/L2 control information transmission part and a non-hatched part serving as a data transmission area.
FIG. 2 is a conceptual diagram illustrating a general method for transmitting data in the E-UMTS system. Generally, the E-UMTS system uses a Hybrid Auto Repeat request (HARQ) technique serving as a data retransmission technique, so that it improves a throughput and performs seamless communication.
Referring to FIG. 2, a base station (BS) transmits downlink scheduling information (also called “DL scheduling information) over a DL L1/L2 control channel (e.g., a physical downlink control channel (PDCCH)), so that it transmits data to the user equipment (UE) according to the HARQ technique. The DL scheduling information may include a UE identifier (ID) or a group ID, resource assignment information allocated to transmit downlink data or duration of assignment information, transmission parameters (e.g., a modulation scheme, a payload size, and MIMO-associated information), HARQ process information, redundancy version information, and a new data indicator.
During the above-mentioned process, a UE ID (or a group ID) such as a radio network temporary identifier (RNTI) is transmitted, such that the UE ID (or group ID) can indicate which one of UEs is used for DL scheduling information transmitted over the PDCCH. The radio network temporary identifier (RNTI) is classified into a dedicated RNTI and a common RNTI. The dedicated RNTI is used to transmit/receive data to/from a UE registered in a Node-B. Provided that no information is registered in a Node-B and the Node-B communicates with UEs having no dedicated RNTIs, the common RNTI is used to transmit or receive common information (or system information) of several UEs. There are a variety of common RNTIs, for example, a RA-RNTI or T-C-RNTI for use in a random-access process over a Random Access Channel (RACH). The UE ID or the group ID may be CRC-masked on the DL scheduling information transferred over the PDCCH.
UEs contained in a specific cell monitor the PDCCH over the L1/L2 control channel using UEs' RNTI information. If the UEs successfully perform the CRC decoding using their RNTI information, they receive the DL scheduling information over a corresponding PDCCH. The above-mentioned UE receives downlink data to be transmitted to the UE itself, over a PDSCH indicated by the received DL scheduling information.
The scheduling schemes can be classified into a dynamic scheduling scheme and a persistent scheduling scheme. The dynamic scheduling scheme transmits the scheduling information to a specific UE over a DPCCH, whenever uplink or downlink resources must be allocated to the specific UE. The persistent scheduling scheme indicates that the Node-B statically allocates downlink or uplink scheduling information to the UE at an initial call setup such as a radio bearer setup.
According to the persistent scheduling scheme, the UE does not receive DL- or UL-scheduling information from the Node-B whenever it transmits or receives data, and uses the scheduling information pre-allocated to the Node-B. For example, provided that the Node-B transmits an RRC signal to a specific UE at the radio bearer setup process, the specific UE will receive downlink data from the Node-B via “A” radio resources according to a “B” transmission scheme during a “C” period by the RRC signal. As a result, the specific UE can receive downlink data from the Node-B using the above “A”, “B”, and “C” information. In this way, although data is transmitted from the UE to the Node-B, the UE can transmit downlink data using predetermined radio resources according to the pre-allocated uplink scheduling information. The above-mentioned persistent scheduling scheme is optimized for a service (e.g., a voice communication service) having regular traffic characteristics.
Voice data formed by an AMR codec (i.e., an audio codec) used for the voice communication service has specialized characteristics. Namely, voice data is divided into a talk spurt and a silent period. The talk spurt is indicative of a period of voice data formed while a user really talks to someone. The silent period is indicative of a period of voice data formed while a user does not talk to someone. For example, a voice packet including voice data in the talk spurt is generated at intervals of 20 ms, and a silence insertion descriptor (SID) packet including voice data in the silent period is generated at intervals of 160 ms.
In the case of applying the persistent scheduling scheme to the voice communication, the Node-B may establish radio resources according to the talk spurt. In more detail, the Node-B may use characteristics indicating that a voice packet is generated at intervals of a predetermined time of 20 ms, and may pre-establish radio resources for transmitting/receiving uplink- or downlink-data at intervals of a predetermined time of 20 ms during the call setup process. In this case, if a current status is changed from the talk spurt to the silent period, the SID packet is generated at intervals of a predetermined time of 160 ms, such that considerable amounts of radio resources, which have been allocated at intervals of 20 ms, are unavoidably consumed.
In this way, it is assumed that the Node-B pre-allocates radio resources to the UE in response to the silent period according to the persistent scheduling scheme such that the UE can use the radio resources at intervals of 160 ms in response to the silent period according to the persistent scheduling scheme. Under this situation, if the UE moves from the silent period to the talk spurt, there is a small amount of allocated resources whereas there are large amounts of voice information to be transmitted by the UE, resulting in the occurrence of a delay of voice information transmission.